When a vehicle is left unoccupied with the windows closed, with the sun shining on it in hot weather, the temperature of air inside the cabin of the vehicle can rise to a value which is substantially greater than the external temperature. For example, when the outside temperature is 45.degree. C., the temperature in the cabin of the vehicle can reach 65.degree. C. It is therefore desirable to reduce the internal temperature before the driver and/or other occupants return to the vehicle.
The direct use for this purpose of an air conditioning apparatus in its normal mode of operation involves considerable expenditure for energy, and quite a long time delay before conditions are restored to a comfortable temperature, that is to say a temperature of the order of 20.degree. C.